Noise spectroscopy with large clouds of cold atoms

TL;DR

This paper investigates how laser frequency noise converts to intensity noise when passing through cold atom clouds, revealing frequency-dependent effects and enabling characterization of both laser and atomic sample properties.

Contribution

It provides a detailed analysis of intensity noise spectra in cold atom clouds and introduces a mean-field model to interpret the noise features, advancing noise spectroscopy techniques.

Findings

Intensity noise spectra collapse at low frequencies

Differences appear at higher frequencies with detuned probe beams

Model successfully explains main spectral features

Abstract

Noise measurement is a powerful tool to investigate many phenomena from laser characterization to quantum behavior of light. In this paper, we report on intensity noise measurements obtained when a laser beam is transmitted through a large cloud of cold atoms. While this measurement could possibly investigate complex processes such as the influence of atomic motion, one is first limited by the conversion of the intrinsic laser frequency noise to intensity noise via the atomic resonance. This conversion is studied here in details. We show that, while experimental intensity noise spectra collapse onto the same curve at low Fourier frequencies, some differences appear at higher frequencies when the probe beam is detuned from the center of the resonance line. A simple model, based on a mean-field approach, which corresponds to describing the atomic cloud by a dielectric susceptibility, is sufficient to understand the main features. Using this model, the noise spectra allow extracting some quantitative informations on the laser noise as well as on the atomic sample.